The present invention relates to a new and improved method for coating fibers, and particularly glass fibers at forming; and to the fibers coated thereby.
The technology which has been developed for the production of glass fibers, presently makes possible the production of fibers having a diameter of from approximately 0.0001 inch to approximately 0.0004 inch, at a rate of from approximately 10,000 feet per minute to approximately 15,000 feet per minute. Glass fibers are produced from small streams of molten glass which exude through tiny orifices located in what is called a bushing. Conventionally, bushings have 204 such orifices. The tiny streams of molten glass which issue from the bushing are attenuated by pulling the fibers until the diameters given above result, and during which time the streams cool and rigidify into what are called filaments. These filaments are then coated with a protective film for the purpose of preventing glass to glass abrasion, and following which they are brought together to form a strand. This strand is coiled upon a spool to form a package. During formation of the package, the strand is traversed back and forth across the spool by a device which is called a traverse, and which is located between the point where the coating materials are applied, and the rotating spool on which the package is made. The spool is rotated by what is called a winding drum, and the pulling action supplied by the winding drum attenuates the molten streams of glass, pulls the filaments past the coating applicator, and through the traverse, and coils the strand onto the package. The winding drum is usually located approximately 10 feet from the bushing, so that the entire forming operation is carried out in a fraction of a second.
The problem of abrasion of glass upon glass is a serious one and has generally been a controlling factor in the rate at which this technology has developed. The seriousness of the problem has caused the wide spread theory that glass to glass abrasion can only be prevented by a solid film of material between the filaments to at all times assure physical separation of the filaments. Regardless of the validity of this theory its acceptance by the art has not caused the art to develop a coating which is completely satisfactory under all conditions for use in separating the filaments during forming. Where the strands are to be woven into textiles, it will be apparent that the amount of film forming materials which can be used must be held within certain percentages of the total weight of the strand in order that the strand will not be unduly stiff. Dyes will not color the glass itself, and so the coatings which are used must either be capable of being dyed, or must be capable of being removed, and later replaced by a material capable of being dyed. Where the glass is to be used for reinforcing plastic materials, the bond between the coatings and the glass filaments is very important, as well as the compatibility of the coating with the later applied resin which the coated strand is intended to reinforce.
The technology in its forty some years of existence has examined all types of materials for their suitability as coatings on glass fibers in an attempt to find one which is "universal" in that fibers coated therewith can be used for all known subsequent uses of coated glass strand. The art has tried all kinds of resins, either as emulsions, or as solutions is organic solvents, but all lack some desired characteristics, and usually suffer from high tensions during weaving operations. In addition, organic solvents create explosion hazards. Explosion hazards require expensive equipment to overcome. In general, resins and other materials requiring organic solvents have not been better than coating materials which are soluble in aqueous media, so that the art has substantially universally used coating materials soluble in water. By and large, the most commonly used coating materials for protecting glass fibers during the forming operation comprise starch in some form. Although starch is not durable to the degree that it can stay in place on the filaments and provide protection after the fibers are woven, it has been without equal in its protection of the strands during the various abrasion producing operations that are involved preparatory to, and during, weaving. In addition, methods have been developed, usually burning, which are quite satisfactory for removing the starch after weaving, so that any desired finish coatings can then be applied. The art has long desired to replace starch base coatings, which are only temporary in nature, with a single coating material which would perform as satisfactory as starch base materials during forming, and which would also act as a finish size which is capable of being dyed and which will permanently protect the filaments during use. The art would further like this coating material to be a "universal" one, so that it can be used regardless of the end use of the strand. Such a universal coating material for glass fibers has never been developed, and there is considerable belief in the art that one will never be developed, because of the great number of properties which such a material must have.
Coating materials, including starch base coating materials, must be quite fluid when applied to the filaments, in order that the coating materials will completely cover, or "wet out" the filaments in the short length of time that exists before they are brought together into a strand. The amount of "solids" that can be applied to the filaments, therefore, is limited by the degree of fluidity necessary to "wet out" the filaments. It is not possible to apply fluid coating materials in an amount which will completely "wet out" the strands without having an excess present, and a high percentage of the coating fluids brought in contact with the filaments is thrown into the surrounding area as a spray. In addition, the coating collects at different areas of the applicator and winding equipment which then either drips or is thrown to the floor. In all prior art processes with which applicants are aware, the degree of fluidity required necessitates that the coating fluids have only a small percentage of solids, and a high percentage of the coating materials that are carried with the strand into the coiled package is the solvent. The coiled packages of strand which are produced must be dried prior to subsequent twisting and weaving operations, and during this drying operation, the movement of the fluid or solvent migrates to the surface of the package and carries along with it some of the solid materials which form the coating. This movement of the solid materials with the solvent is commonly called "migration." The art has long been concerned with the problem of migration and a considerable number of patents have been concerned solely with this single problem.
According to the concept of the present invention, a new and improved method of applying coating materials to fibers, and particularly glass fibers at forming, is provided which will allow the various already developed coating materials to be applied to the fibers in a manner which overcomes some of the problems which the prior art has tried to overcome by specially developed coating materials.
Accordingly, it is an object of the present invention to provide a new and improved method of applying coating materials to glass fibers at forming which substantially eliminates the spray and other types of loss of the coating material to the surrounding area.
Another object of the invention is the provision of a new and improved method of applying coatings to fibers which will allow a greater "concentration" of solids to be applied to the fibers.
Another object of the invention is the provision of a new and improved method of applying coatings to glass fibers at forming which substantially completely overcomes the problem of "migration."
A further object of the invention is the provision of a new and improved method of coating glass fibers, and particularly glass fibers at forming, wherein the coating material is either a reversible shear thinning gel, or is contained within a reversible shear thinning gel, and the coating material is caused to flow around the fibers as a liquid and then revert to a gel.
Further objects and advantages of the invention will become apparent to those skilled in the art to which it relates from the following description of the method of the present invention, as well as numerous examples of materials which can be applied to the fibers according to the method of the invention.